Which electronic configuration is common to all actinoid elements?

The number of $f$-electrons in the $+3$ oxidation state of gadolinium $(Z=64)$ is $x$ and in the $+2$ oxidation state of ytterbium $(Z=70)$ is $y$. The sum of $x$ and $y$ is:

Which of the following statements is not correct regarding lanthanoids?

Consider the following statements:
$I$. $La(OH)_3$ is the least basic among hydroxides of lanthanides.
$II$. $Zr^{4+}$ and $Hf^{4+}$ possess almost the same ionic radii.
$III$. $Ce^{4+}$ can act as an oxidizing agent.
Which of the above is/are true?

Identify the strongest base from the following.

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $5f$ electrons can participate in bonding to a far greater extent than $4f$ electrons.
Reason $R$: $5f$ orbitals are not as buried as $4f$ orbitals.
In the light of the above statements,choose the correct answer from the options given below: